1. Field of the Invention
The present invention relates to a system for use with wells drilled into the earth's crust. More particularly, the present invention relates to a support apparatus for conducting downhole operations in wells including, without limitation, cutting underwater casing strings and retrieving tubular goods from wells.
2. Description of the Prior Art
Oil and gas wells are typically drilled using drilling rigs or other similar devices to create substantially cylindrical boreholes that extend downward into the earth's crust. After a well has been drilled to a desired depth, large diameter pipe commonly referred to as casing is frequently installed into the well and cemented in place. Thereafter, production tubing is often run into the well, concentrically inside the casing, in order to provide a conduit for the flow of oil and/or gas production from an underground reservoir to the earth's surface.
It is often necessary to conduct downhole operations within a well for any number of reasons including, without limitation, remedial or repair work. In such instances, it is often beneficial to insert tubular goods and bottom-hole assemblies into said well, manipulate (for example, rotate or reciprocate) said tubular goods and bottom-hole assemblies within said well, and/or remove tubular goods and other equipment from said well.
In order to perform such downhole well operations, it is frequently necessary to provide a surface structure for supporting equipment and personnel. Although conventional drilling rigs can generally be used for this purpose, the expense associated with mobilization, demobilization and operation of conventional rigs can be cost prohibitive especially for relatively small operations. Further, space limitations can sometimes prohibit the use of certain larger drilling or workover rigs. Thus, there is a need for a surface support structure that provides some or all of the operational benefits of conventional rigs, such as the ability to rotate tubular goods and lift such tubular goods in and out of a well.
One common downhole operation involves the plugging and abandonment of depleted wells. After hydrocarbon reserves in a well have been fully recovered, the well must eventually be plugged and abandoned and the well site restored to its original condition. Generally, surface equipment must first be removed from a depleted well. Thereafter, as much production tubing and casing as possible is typically retrieved from a well; in many cases, such recovered tubular goods can be reused in other wells or sold for salvage. However, because the pipe—and especially the casing—can be cemented or otherwise secured in place, blades or other cutting devices are frequently needed to cut the pipe at a desired depth in the well prior to removal. In many cases, such cutting equipment is conveyed in and out of a well via tubular workstring. After desired down-hole cut(s) are made, the workstring and the severed pipe are typically pulled out of the well from the surface.
Such plugging and abandonment operations can be expensive, especially when performed using conventional rigs. When conventional rigs are used, such rigs and related equipment must be mobilized to a location prior to commencing work, and demobilized after such work is completed. Even when conventional rigs are not utilized, such plugging and abandonment operations typically require the use of valuable offshore rig space, operation of pedestal cranes and/or other platform-mounted equipment.
Thus, there is a need for an apparatus that eliminates many of the problems associated with conventional well operation techniques including, but not necessarily limited to, plugging and abandonment operations. Such apparatus should support wellbore tubular goods and related equipment that can be used to conduct down-hole operations in oil and gas wells, while requiring minimal surface area (e.g., deck space) and providing many of the operational benefits of conventional drilling and/or workover rigs.